Crossed-field microwave devices with gun shielding means



CROSSED-FIELD MICROWAVE DEVICES WITH GUN SHIELDING MEANS J.- AR-NAUDApril 29, 1969 Filed Aug. 10. 1965 INVENTORI J-AR/VAl/D mm ATTORNEUnited States Patent 3,441,782 CROSSED-FIELD MICROWAVE DEVICES WITH GUNSHIELDING MEANS Jacques Arnaud, Paris, France, assignor to CSF-CompagnieGenerale de Telegraphic Sans F il, a corporation of France Filed Aug.10, 1965, Ser. No. 478,576 Claims priority, applicgationogrance, Aug.26, 1964,

Int. Cl. H01 25/34 U.S. Cl. SIS-3.5 7 Claims ABSTRACT OF THE DISCLOSUREThe present invention relates to microwave devices and more particularlyto crossed-field tubes.

It is known that in the functioning of various types of crossed-fielddevices very often the following perturbations are noticed:

Spurious oscillations in travelling wave tubes,

Discontinuities in the frequency bands in backward wave oscillators(Carcinotrons),

Sudden variations of the noise spectrum in noise generators.

A crossed-field tube generally comprises, within an evacuated envelope,a wave delay line for propagating a microwave, an electrode called sole,defining with the delay line a wave and electron interaction space, anelectron gun producing and injecting into the interaction space a beamof electrons, and a collector electrode that collects the electron-s ofthe electron beam.

Now it has been found that the above-mentioned perturbations are due tothe detrimental action exerted upon the cathode by the unit composed ofthe delay line and the sole electrode, which unit propagates themicrowave energy.

The present invention has as its object to suppress or at leastconsiderably reduce the above-mentioned detrimental action, and to thiseffect a crossed-field tube in accordance with the invention is providedwith an electrostatic shield. located between the electron gun and thesole electrode and carried preferably at the potential of the metallicenvelope of the tube.

Accordingly, it is an object of the present invention to preventspurious oscillations in travelling wave amplifier tubes.

Another object of the present invention is to suppress frequency banddiscontinuities in backward wave oscillators.

Still another object of the present invention is to avoid suddenvariations of the noise spectrum in crossed-field type noise generators.

These and further features, objects and advantages of the presentinvention will be more clearly understood from the following descriptionwhen taken in connection with the accompanying drawing, which shows, forpurposes of illustration only, one embodiment of a crossedfield tube inaccordance with the present invention, FIG- URE 1 being a cross-sectiontaken along line I--I of FIGURE 2 and FIGURE 2 a cross-section takenalong line IIII of FIGURE 1.

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The tube, represented in the two figures, comprises within an evacuatedenvelope 1, a wave delay line 2, an electrode 3, referred to as soleelectrode, parallel to the line 2, a collector 4, and an electron gunincluding a cylindrical cathode 5, a positive electrode 6 and a negativeelectrode 7.

A source of potential E makes it possible to set the various electrodesat suitable potentials, while a magnet NS produces within the tube amagnetic field parallel to the axis of cathode cylinder 5.

The enumerated elements form the well known structure of a crossed-fielddevice. In operation, the electrons emitted by cathode cylinder 5, whichis heated by suitable means (not shown), form a beam 8, indicated indash lines. The beam penetrates into and propagates through theinteraction space comprised between line 2 and sole 3 and impinges uponcollector 4. The functioning is based, as known, on the interactionbetween the electron beam and an electromagnetic wave that propagatesalong the delay line 2 with a speed substantially equal to that of theelectrons.

In accordance with the present invention, the tube structure is improvedby the addition of a metallic shield or screen, located between theelectron gun and the sole.

In the illustrated embodiment, the shield comprises a partition 9, madeup by the major portion of a cylinder, covered at the top (FIGURE 2) bya plate 10 and extending at the bottom into an annular element or ring11. Plate 10 and ring 11 are in contact with the upper and lower wallsof envelope 1, respectively, thereby setting the shield at the potentialof the metallic envelope 1.

This disposition results in a considerable reduction of the couplingbetween the electron gun and the assembly or unit comprising the delayline and the sole. Under these conditions it has been found that thevarious perturbations indicated above are eliminated or considerablyattenuated.

While I have shown and described one embodiment in accordance with thepresent invention, it is understood that the same is not limited theretobut is susceptible of numerous changes and modifications as known to aperson skilled in the art, and I therefore do not wish to be limited tothese details but intend to cover all such changes and modifications asare encompassed by the scope of the appended claims.

I claim:

1. A crossed-field tube comprising within an evacuated, metallicenvelope, a wave delay line and a sole electrode extending substantiallyparallel to each other and defining therebetween an electron and waveinteraction space, an electron gun adapted to produce and inject intosaid interaction space an electron beam, and an electrostatic shieldlocated between said electron gun and the assembly composed of said soleelectrode and said delay line.

2. A crossed-field tube as claimed in claim 1, wherein saidelectrostatic shield is set substantially at the same potential as saidmetallic envelope.

3. A crossed-field electron-discharge device, comprising within anenvelope:

first means including wave retarding and sole electrode means definingan interaction space,

second memans including electron emissive means for producing anelectron stream moving through said interaction space,

collector means for the electrons in said electron stream,

and shield means effectively shielding said electron emissive means withrespect to said first means.

4. A crossed-field electron-discharge device, comprising within anenvelope:

first means including wave retarding and sole electrode means definingan interaction space,

second means including electron emissive means for 5 substantiallyparallel to each other defining therebetween producing an electronstream moving through said interaction space,

collector means for the electrons in said electron stream,

and shield means effectively shielding said electron emissive meanswitth respect to the sole electrode means of said first means.

5. In a crossed-field device having, within an evacuated envelope, awave retarding structure and a sole electrode defining therebetween aninteraction space, means for producing within said interaction spacesubstantially crossed electrostatic and electromagnetic fields, andmeans including electron-emissive means for producing an electron beammoving through said interaction space,

the improvement essentially consisting of electrostatic shield meansefiectively shielding said electron emissive means with respect to atleast one of the two parts consisting of said wave retarding structureand said sole electrode.

6. In a crossed-field device having, within an evacuated envelope,, awave retarding structure and a sole electrode defining therebetween aninteraction space, means for producing within said interaction spacesubstantially crossed electrostatic and'electromagnetic fields, andmeans including electron-emissive means for producing an electron beammoving through said interaction space,

the improvement essentially consisting of electrostatic an elongaatedelectron and wave interaction space, an electron gun positioned at oneend of said interaction space for directing an electron beam therein, acollector electrode positioned adjacent said interaction space forcollecting said electron beam, an electrostatic shield located betweensaid electron gun and the assembly composed of said sole electrode andsaid delay line, and means for generating crossed electric and magneticfields in said interaction space transverse to the path of propogationof said electron beam.

A Gun and Focusing System for Crossed-Field Traveling-Wave Tubes byWatkins et a1. IRE Transactions on Electron Devices Jan. 1959, volumeED-6, No. 1, pps. 18-27, relied upon TK 7870 I-2.

HERMAN K. SAALBACH, Primary Examiner.

SAXFIELD CHATMON, ]R., Assistant Examiner.

US. Cl. X.R.

